As the demand for the telecommunications/server power grows exponentially, the need for higher power density IC devices and power management devices increases each year. Increasing power density relies on less component counts, smaller reactive component size, and/or better system efficiency, among other factors. For a switched mode power supply, higher switching frequency leads to smaller reactive and filter component sizes. Better efficiency, which reduces the size of and/or need for a heat sink or paralleled devices, requires a reduction in conduction losses and/or switching losses.
The use of high-frequency power management in an IC improves power density and reduces form factor, and is thus desirable. In one illustrative application, high-frequency power conversion increases a transit rate which thereby facilitates dynamic scaling of the input power for the load based on the needs of the load. This can reduce power consumption of the load by up to fifty percent.
To increase the switching frequency, high-speed power devices (e.g., greater than about 500 MHz) are generally required. Operating at high frequencies in a power converter is often limited by series inductance in the loop and the reverse recovery behavior of the power switching device used. For example, when a high-speed power device is operating at a high switching speed in a DC-to-DC converter, reverse recovery charge (Qrr) of a low-side power metal-oxide-semiconductor field-effect transistor (MOSFET) will cause high ringing voltages at a switching node in the circuit. One conventional approach to accommodate the high ringing voltage of the switching node is to use a device with high breakdown voltage (BV). However, the high breakdown voltage device will, in general, deteriorate the performance, increase device area, and increase the cost for the device.
There have been various attempts to reduce the switching node ringing voltage. One way to reduce the switching node ringing voltage is to slow down the turn-on speed of a high-side MOSFET. However, doing so will increase the turn-on duration and increase turn-on loss which, in turn, will deteriorate the efficiency of the power conversion and defeat the purpose of the high-frequency switch. Another way of reducing the ringing voltage is to decrease the Qrr of a low-side MOSFET by reducing the p-type body doping concentration in the device, which can lower the threshold of the MOSFET and allow the channel to flow more current during the dead time. However, having a lower p-body doping level makes the device more susceptible to a parasitic bipolar transistor being triggered, thereby causing a failure in the power system.